The regulation of exhaust gas of internal combustion engines such as engines of motor vehicles is gradually tightening in all the world, and under the circumstances, exhaust-gas recirculation systems (so-called EGR: Exhaust Gas Recirculation) are being used, which recirculates exhaust gas to intake for reducing NOx contained in the exhaust gas. For example, there has been suggested, e.g., an exhaust-gas recirculation system including a takeoff passage of exhaust gas communicating with an exhaust port in an internal combustion engine; an introducing passage communicating with an intake port of the engine; an opening and closing valve provided between the takeoff passage and the introducing passage; and a control means for controlling an opening and closing operation of the opening and closing valve; wherein the exhaust-gas recirculation system is arranged such that the introducing passage is branched, on an outlet side of the opening and closing valve, correspondingly to the number of the exhaust port of the internal combustion engine (see Patent Document 1, for example).
Technological contents disclosed in this Patent Document 1 is that exhaust gas from an EGR passage admitted to a source of exhaust is introduced, through an EGR valve, into a plurality of air-gas intake passages provided, correspondingly to the number of cylinders of the internal combustion engine.
In the engine having such an arrangement, it has an fear of an aggravation originated from fall-off of negative pressure (getting near to the atmospheric pressure) at the intake port, caused by taking an intake in another cylinders, which invites lowering of the amount of air to be taken in by inertia.
Patent Document 1: JP-A62-294757
The conventional exhaust-gas recirculation system is thus arranged as mentioned above, and therefore, the EGR-gas introducing passages thereof are in communication with one another between mouths of a plurality of inlet valves located at positions spaced away from the valve. Therefore, the communication with another inlets through another EGR gas introducing passages incurs an aggravation of an intake efficiency, when observing an arbitrary EGR-gas introducing passage.
The present invention has been made to solve the above-mentioned problem, and an object of the present invention is to provide an exhaust-gas recirculation system able to ravel out the aggravation of the intake efficiency with a simple mechanism.